This invention relates to a flexible control valve, and more particularly, to a duckbill-umbrella valve for regulating fluid flow in each of two directions.
Duckbill valves, such as the type disclosed in U.S. Pat. No. 3,155,110 and U.S. Pat. No. 3,159,176, are well-known and generally operate effectively at relatively low pressures. At back pressures or head pressures below a desired opening pressure, however, the duckbill elements may spread apart causing undesired fluid flow.
In a typical operation of a fluid transfer device using a duckbill-umbrella valve, the umbrella portion of the valve regulates the flow of a primary solution of medicament to a pump or syringe. The duckbill elements regulate the flow of fluid transferred from the pump or syringe to the patient. When the syringe is raised or elevated to the desired position, a pressure head may build up and cause the duckbill elements to separate, thereby allowing undesired gravity flow of the syringe-fluid to the patient. When a relatively high pressure pump is used instead of the syringe, head pressures may be even greater. Excessive back pressures may develop, causing the duckbill elements to separate and allowing undesired backflow of fluid from the patient to the pump. Excessive back pressures may cause body fluids to be sucked out or withdrawn from the patient, and such withdrawal of body fluids from a patient without the supervision of a physician is extremely dangerous.
U.S. Pat. No. 3,710,942 illustrates a highly porous foam insert bonded to a duckbill valve. This construction is suggested as a means for providing additional biasing force to prevent the duckbill elements from opening until a certain pressure is reached. It has been found, however, that this type of valve is relatively expensive to manufacture. The density of the foam or sponge is difficult to control within a desired range, which results in the production of duckbill valves having different densities and which open at different pressures rather than one desired pressure. Furthermore, it is very difficult to control the radial dimension of the highly porous foam within a desired tolerance, which results in duckbill valves of different sizes.
In operation, the sponge or foam insert described in U.S. Pat. No. 3,710,942, may not provide sufficient biasing force to prevent the duckbill elements from opening at a pressure head as low as one psi. Furthermore, thick viscous solutions do not readily flow through the flow passageway of the valve.
When it is desirable to have a valve open at a predetermined pressure, such as 42 inches of water head, the previously described prior art valves may be ineffective causing undesired fluid flow at pressures as low as 36 inches of water head.
It is, therefore, an object of this invention to provide a duckbill-umbrella valve that operates satisfactorily to prevent flow until a predetermined amount of pressure is achieved.
Other objects of this invention are to provide a safety valve which is dependable in operation, relatively inexpensive to manufacture, easily installed and removed from operating position, and capable of performing properly after long periods of use.
These and other objects will become apparent from the following description and appended claims.